There are times when battle gets full and during those times imms/leaders might start creating additional requirements like being deadly/active to keep your spot. Likely Abernyte was referencing one of those times. It's really not much different than when any cabal gets full and you start being more selective about applicants and pay more attention to the qualities of current members.


There are also times when mortal leaders believe PK ability is part of being the greatest warriors in thera and may incorporate that into the way they run the village but its not a "tradition" so to speak that a player must be a good PKiller to be a berserker.